The invention relates to a thermomagnetic circuit breaker having a selective trip display.
Circuit breakers in a preformed or cast housing with thermomagnetic tripping means are well known in commercial and industrial applications. U.S. Pat. No. 3,162,739 discloses a means of this kind which has a bimetallic strip for thermal trip resulting from overload currents and a magnetic element for instantaneous trip resulting from short-circuit current surges. The tripped state is displayed by the particular position of the operating handle, as is indicated in U.S. Pat. No. 3,158,717.
A means for providing a visual display of an overload condition (reason for trip) in a thermomagnetic circuit breaker is disclosed in U.S. Pat. No. 3,883,781 and U.S. Pat. No. 5,519,561. The systems described therein use either mechanical or electrical logic information, provided by the bimetallic strip, to execute and produce a display of the overload condition. If such a device is equipped only with overload and momentary reaction elements (trip elements), a selective trip display is provided, where an instantaneous trip reaction exists when the operating handle designates the "tripped" state and the overload display system is not activated.
The increasing significance of electronic circuits as suitable devices for the display of overcurrents in electric line protective means has likewise made possible devices for distinguishing between the reasons for a trip. Printed source U.S. Pat. No. 5,485,343 describes an electronic trip unit for a circuit breaker which permits the user to determine the intensity of as well as the reason for the overcurrent condition after occurrence of the overcurrent trip. The electronic trip display for such trip information is similar to the display described in U.S. Pat. No. 4,870,531, and the control unit for such an electronic trip unit is like the trip unit described in U.S. Pat. No. 4,672,501.
In U.S. Pat. No. 3,158,717 the reason for occurrence of a disconnect condition, be it because of overload or due to a momentary overcurrent, is not indicated.
In U.S. Pat. Nos. 3,883,781 and 5,519,561, however, the devices are unable to provide a selective trip display if more than two trip elements, such as with reference to an overload, a momentary trip, a ground fault or an accessory trip (trip due to additional structural components or accessories), are provided.
The additional functions available in circuit breakers having electronic trip units, such as U.S. Pat. No. 4,870,531, however, do not always justify the additional costs for the components of electronic trip units.
Thus there is a particular need to design a thermomagnetic circuit breaker so that upon trip of the thermomagnetic circuit breaker the reason for trip is displayed in simple fashion.